1. Field of the Invention
The present invention relates in general to semiconductor surface preparation, and in particular to the use of dissolved ozone to perform cleaning, etching, and stripping operations.
2. Background
During the wafer fabrication process, manufacturers found ozone to be a particularly useful active reagent. For example, manufacturers use ozone in at least the operations of sterilizing process chambers and wafers, etching oxides, stripping off photoresist material, and the like. For example, in one approach for removing photoresist from a workpiece, a manufacturer uses ozone to loosen undesired portions of photoresist. The manufacturer then washes the undesired portions of photoresist from the workpiece.
Because manufacturers repeat these operations many times in order to form complex semiconductor devices, it is important to maximize the efficiency of the ozone reaction with a workpiece, thereby increasing the speed of overall wafer fabrication. One way to increase the efficiency of the ozone reaction is to increase the overall amount or concentration of ozone that reaches the workpiece.
The concentration of ozone reaching the workpiece is adversely affected by, among other things, ineffective transport of ozone to the workpiece and interfering byproducts of the ozone reaction. In order to overcome such adverse affects, manufacturers discovered that water not only acts as a transport solution, but also washes away the interfering byproducts of the ozone reaction. Accordingly, manufacturers began using immersion tanks for operations that involved ozone reactions. In general, immersion tanks immerse the workpiece in a solution, e.g., ozone-enriched water, in order to provide ozone reactions. However, immersion tanks provide less efficient ozone transportation because although water does transport ozone, water also quickly decomposes some of the ozone into a useless solution. Therefore, water generally has an upper limit on a steady state of ozone concentration. In addition, immersion tanks do not wash away the interfering byproducts efficiently because the solutions in immersion tanks are relatively stable.
Therefore, manufacturers developed a xe2x80x9cspin and sprayxe2x80x9d process in order to overcome the drawbacks of immersion tanks. In the spin and spray process, manufacturers spin the workpiece at high velocities while spraying water onto the workpiece in an ozone-enriched ambient. The velocity of the spinning workpiece controls the thickness of a water boundary layer formed thereon. By controlling the thickness of the water boundary layer, the manufacturers attempted to reduce the ability of the water to decompose the ozone before the ozone could reach the workpiece. This reduction in the ability of the water to decompose ozone helps provide ozone concentrations above the typical limit of the water.
However, the spin and spray process has a variety of drawbacks. For example, in order to provide the desired water boundary layer thickness, the workpiece needs to spin at velocities greater than approximately 800 rpm. Such spinning requires a large amount of mechanical complexity and poses a significant risk of damage to the workpiece. While mechanical complexity greatly increases the cost of the process chamber, damage to the workpiece lowers yield rates.
All of the above mentioned drawbacks give manufacturers the undesirable choice between using a low concentration of ozone, thereby substantially slowing overall wafer fabrication, or increasing the concentration of ozone, thereby greatly increasing the overall cost and risk.
One aspect of the invention is to provide an apparatus and method for delivering highly concentrated dissolved ozone to a workpiece in order to increase the ozone reaction therewith. According to one embodiment, the apparatus includes a process chamber employing an array of spray nozzles that spray a thin water boundary layer onto the workpiece. The water boundary layer transports ozone from the ozone-rich ambient to the workpiece. According to this embodiment, the workpiece is held substantially stationary.
According to another embodiment, fluid is pulsed through the spray nozzles. According to yet another embodiment of the invention, the pulsing of the water comprises a limited duty cycle. According to yet another embodiment, the wafers are slowly rotated to ensure the water boundary layer on the workpiece is sufficiently uniform.
The pulsing of water through the spray nozzles advantageously increases the water""s ability to wash away the interfering byproducts of the ozone reaction without increasing the overall amount of water used. This is advantageous because it allows the water boundary layer on the wafers to be very thin. The thin water boundary layer transports ozone from the ozone-rich ambient to the workpiece without supplying enough water to detrimentally decompose the ozone. Thus, highly concentrated dissolved ozone reacts with the workpiece without including the drawbacks of mechanical complexity and risk associated with the spin and spray process.
In one embodiment, an apparatus comprises a pulsator that pulses a solution into an ozone-rich environment to create an ozone-rich solution. In another embodiment, an apparatus comprises a sprayer that periodically pulses an ozone-rich solution onto a wafer.
In yet another embodiment, an apparatus comprises a rotating platform that is configured to rotate the workpiece. The apparatus further comprises a pulsator that pulses a solution into an ozone-rich environment to create an ozone-rich solution on the workpiece. In an additional embodiment, the apparatus pulses an ozone-rich solution onto the workpiece.
One aspect of the invention relates to a method for stripping a layer from a semiconductor wafer. The method comprises introducing ozone into a process chamber and activating a water spray for a first predetermined amount of time, thereby creating a water layer on a semiconductor wafer, wherein the water layer transports high concentrations of the ozone to the semiconductor wafer. The method further comprises deactivating the water spray for a second predetermined amount of time, thereby controlling a thickness of the water layer; and re-activating and re-deactivating the water spray until the ozone substantially removes portions of the layer from the semiconductor wafer.
Another aspect of the invention relates to an ozone shower system that comprises an ozone source. The ozone source is configured to supply ozone to a process chamber. The ozone shower system also comprises a sprayer connected to a fluid source such that fluid sprays over a workpiece in the process chamber. The ozone shower system further comprises a pump connected to the fluid source, and a selector valve connected to the pump. The selector valve is configured to selectively pulse the fluid through the sprayer.
An additional aspect of the invention relates to a method that comprises introducing a reagent to an ambient and activating a solution spray in the ambient for a first time period. The method also comprises deactivating the solution spray for a second time period, thereby increasing the efficiency of a reaction of the reagent and a workpiece.
Another embodiment of the invention is a reaction chamber that comprises a gas input and a plurality of nozzles connected to a nozzle manifold. The reaction chamber further comprises a wafer cartridge that holds wafers. The reaction chamber also comprises a first fluid line connected to the nozzle manifold. In addition, a second fluid line is configured to divert water flow away from the first water line.
Yet another embodiment of the invention is a reaction chamber that comprises at least one nozzle connected to a fluid supply wherein the nozzle is configured to pulse fluid onto a workpiece. The reaction chamber also comprises a rotator that rotates the workpiece at a velocity ranging from approximately 100 rpm to stationary.
Another aspect of the invention relates to an apparatus that comprises at least one wafer-processing chamber wherein an ozone rich environment exists within the wafer-processing chamber. The apparatus further comprises a sprayer, and a pulsating fluid source. The pulsating fluid source is configured to pulse a solution through the sprayer into the ozone rich environment.
An additional aspect of the invention relates to an apparatus that comprises at least one semiconductor processing chamber and a pulsating fluid source. The pulsating fluid source is configured to pulse an ozone-rich solution into the semiconductor processing chamber.
Yet another aspect of the invention relates to a method that comprises introducing a reagent into an ambient, and pulsing a solution spray in the ambient, thereby increasing the efficiency of a reaction of the reagent.
Another embodiment of the invention relates to an ozone shower system that comprises a process chamber and a pump. The pump is connected to the process chamber and configured to pulse a solution into the process chamber.
For the purposes of summarizing the invention, certain aspects, advantages and novel features of the invention have been described herein above. Of course, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. Other aspects and advantages of the invention will also be apparent from the detailed description below and the appended claims.